The common notchbacks have open rear truck beds which have a poor protection for shipments. During transportation, goods would be damaged or contaminated by dust due to wind and rain. When running under poor road conditions, the goods tend to be tossed and fall out due to jolt. And when parking, the goods in the rear truck bed with an open structure are easier stolen or lost. With regard to this, people install a movable cover plate to cover and close the rear truck bed, and remove the cover plate only when the goods are comparatively high. Existing cover plates that are made of resin for glass fiber reinforced plastic or thermoplastic plastics are very inconvenient for use, wherein the cover plate made of glass fiber reinforced plastic resin must have a certain thickness to ensure sufficient strength. If the cover is too thick and heavy, it will affect the opening-closing flexibility and have a high requirement to the actuating mechanism. The cover plate made of thermoplastic plastic has a hollow structure, but the thickness of the cover is large and it occupies too much room of the rear truck bed.